Fusion welding is welding process used to join (i.e., fuse) two or more pieces of metal by causing the metal to reach its melting point. The process typically involves the use of a filler metal, provided by a consumable electrode or a wire, and a flux, which protects the molten metal of the weld from the damaging effects of the atmosphere. Fusion welding is utilized in numerous industries, including the oil and gas sectors, the energy industry, light and heavy manufacturing operations and the aerospace industry. There are several types of fusion welding processes, including arc welding, electric resistance welding, oxy-fuel welding and thermite welding, as well as certain advanced and high production rate joining processes, including laser-beam welding combined with gas-metal-arc welding (LBW/GMAW), also known as hybrid laser gas metal arc welding (HLGMAW). Due to the high-temperature phase transitions inherent in these processes, a heat-affected zone is created in the welded material. Because fusion welds often encounter significant loads and fatigue during the lifetime of a welded product, there is a chance that such welds may fail if not created to proper specifications. For example, the base metal must reach a certain predetermined temperature during the welding process, must cool at a specific rate, and must be welded with compatible materials or the joint may not be strong enough to hold separate parts together or cracks may form, thereby causing the weld to fail. Common welding defects such as lack of fusion (LOF) of the weld to the parent metal, cracks or porosity inside the weld, and variations in weld density may cause a structure to fracture and break or a pipeline to rupture. Accordingly, inspecting such welds after their creation is an important aspect of preventing the failure of welded products.
Fusion welds may be tested using non-destructive evaluation techniques such as visual inspection; industrial radiography or industrial computer tomography (CT) scanning using X-rays or gamma rays; ultrasonic testing; liquid penetrant testing; magnetic particle inspection; or by eddy current. In a proper weld, these tests would indicate a lack of volumetric (pores, undercut, under-fill etc.) defects in a resultant radiograph, show clear passage of sound through the weld and back, or indicate a clear surface without penetrant captured in cracks. However, the detection of transverse discontinuities is very difficult with existing ultrasonic equipment, and the various techniques currently applied require that welding equipment be removed to conduct post-weld non-destructive evaluation. Removing the welding equipment often causes delay in the welding process and creates additional fabrication and examination delays if unacceptable discontinuities are detected which require repair or re-examination. Thus, there is an ongoing need for a more efficient, less disruptive system and method for conducting non-destructive evaluation of fusion welds for quality assurance. More particularly, there is a need in the art for an approach for real- or near-real time weld monitoring of joining process such as HLGMAW whereby analyses can be done during fabrication.